1. Field of the Invention
The present invention relates to a security keyboard with contacting means, a plurality of keys and a switching foil, where the contacting means has contact elements required for the security keyboard and is substantially completely enclosed in a security film and the keyboard pressure on operating the plurality of keys is transmitted through the security film to the contact elements of the contacting means.
2. Description of the Related Art
At the present time a range of equipment is employed for electronic funds transfer (EFT or electronic cash) for data entry or output. Certain security provisions are associated with this equipment in order to be able to avoid any possible undesired manipulation. The security of confidential information and the protection of data input and output from possible influences or manipulation is generally effected by means of electronic or mechanical security measures, such as, for example, the physical incorporation of various security-relevant components into one security module. Particularly security-sensitive components or modules are, in particular, data displays for data output, data input keyboards, key memory for storing confidential keys, e.g. for coding data transfer and security circuits for electronic protection of security-relevant components. Thus, keyboards in particular, have to be protected against simultaneous disclosure of input data, such as a personal identification number (PIN).
A security module for an electronic funds transfer system is known from European Patent Application EP A-0186981. The security module is located in an impact-resistant housing. The module has a PIN entry block and can key confidential data, such as, for example, the PIN, and thus offers access to these data to other equipment.
An extensive study of the physical security of systems for an electronic funds transfer is known from the IBM document "Physical Security for the IBM Transaction Security System", IBM Charlotte, North Carolina, 28257, 6th May 1991 by G. P. Double. This document proposes various test methods and possible protective measures. In particular, this document teaches the use of a so-called Intrusion Detection Screen for the electronic detection of mechanical penetration of the film. The intrusion detection screen comprises a flexible circuit board with thin meandering conductor paths. If the conductor paths are short-circuited or destroyed by mechanical action, such as, for example, penetration or tearing, this will be recognized by one of the in-built security switches. A monitoring logic connected to the intrusion detection screen recognizes changes in the resistance network of the protective film and sets off a suitable alarm which can lead, for example, to the deletion of security-relevant data.
To make manipulations at keyboards, which are intended, for example, for use in electronic funds transfer, more difficult, a range of measures is known which will enhance data security. A known method for this is to encapsulate the electronics to be protected, including the keyboard.
Apart from the encapsulation method, it is also usual to embed the security logic with data memory and the keyboard required for data input, in a housing and to wrap the housing in a security film. The security film is here designed in such a way that removal of or damage to the security film will lead to a corresponding alarm.
Apart from the data memory, which contains any security-relevant data, the keyboard must be protected so as to prevent or make more difficult the unauthorized `theft` of the information input, such as, for example, a personal identification number (PIN). Total encapsulation of the keyboard, however, is not possible, since the keyboard must be at least partially accessible for input.
An arrangement is known from the IBM Technical Disclosure Bulletin, Vol.33, No.9, February 1991, pp. 448-449, in which the contact portions of the keyboard are disposed within a region protected by a security film while the keys themselves remain outside the protected region and are thus accessible to the user. It is a problem with this arrangement, however, that the security film opposes the pressure from the keyboard keys, so that the keys require increased pressure. This can, however, place greater mechanical demands on the security film. With repeated operation of the keys, the effects of wear are so marked that the working life of the equipment may be severely reduced. Positive operation of the keyboard can frequently not be ensured because of the greater force required.
In order to be able to avoid the aforementioned disadvantage of the greater force required on the keys of the keyboard brought about by the security film, there are arrangements in which the switches within the security film are operated through an opening in the security film by means of a plastic plunger. FIG. 1 shows an arrangement of this type in accordance with the state of the art. Such a keyboard has a circuit board 1 and a key 2. The circuit board 1 contains the necessary electronics for the keyboard while the key 2 acts on the circuit board to produce the signals. The circuit board 1 is completely within a housing 3 and underneath a security film 4. The key 2 partly juts out above the housing 3 and is returned to a defined starting position by means of a return spring 5. Within the security film 4 there is an aperture 6 through which a plunger 7 from the key 2 can act on the circuit board 1. After operation of the key 2, the latter is returned by means of the return spring 5 to the starting position.
It is, however, a disadvantage of this arrangement that the security film must have a plurality of openings, one for each key. As a consequence, the degree of security is significantly reduced, since penetration is possible into the security region through the apertures 6. This again requires expensive security measures to minimize the danger of possible intrusion through the security film.